Registering a MediatR pipeline constrained PostProcessor using ASP.NET Core DI

Question

Previously, we had the following pipeline setup working for auditlogging purposes

    public class AuditLogPostProcessor<TRequest, TResponse> : 
           IRequestPostProcessor<TRequest, TResponse> 
              where TRequest : IAuditLogRequest<TResponse>

Where IAuditLogRequest implements IRequest

public interface IAuditLogRequest<TResponse> : IRequest<TResponse>

All and only the Commands that implement the IAuditLogRequest reached the AuditLogPostProcessor.

Registration using SimpleInjector was as follows

_container.RegisterCollection(typeof(IRequestPostProcessor<,>), 
    new[] { typeof(GenericRequestPostProcessor<,>),typeof(AuditLogPostProcessor<,>) });

Currently, we use the ASP.NET Core DI for our Dependence Injection with the following registration.

services.AddScoped(typeof(IRequestPostProcessor<,>), typeof(GenericRequestPostProcessor<,>));
services.AddScoped(typeof(IRequestPostProcessor<,>), typeof(AuditLogPostProcessor<,>));

When a Command implements the IRequest, we get the error

TypeLoadException: GenericArguments[0], 'Command', 
on 'AuditLogPostProcessor`2[TRequest,TResponse]' violates 
the constraint of type parameter 'TRequest'.

So it seems the DI is not honoring the constraint. Can I get the desired behavior with the ASP.NET Core DI?

Answer 1

I was looking to do exactly the same thing. Apparently ASP.net core DI does not support this feature.

SRC: Support constrained open generic types

You need to use another container such as Autofac or StructureMap. Example: Autofac for ASP.NET core

It's very simple and it does not require much changes